如何通过结构重新格式化JSON？

Question

I have pulled some data out of a given database - the format however is not correct as per what I want.

Sample struct:

type myStruct struct {
    ID                  int    `json:"Id"`
    Language            string `json:"Language"`
    Location            string `json:"Location"`
}

Right, I serialize a given map of strings with a custom struct representing the given returned columns:

func transformJSON(extract []map[string]*sql.SqlCell) ([]byte, error) {
    return json.MarshalIndent(extract, "", " ")
}

This returns valid JSON, but with the format:

  {
      {
      "id": {
       "Value": {
        "Long": 12353
       }
      },
      "language": {
       "Value": {
        "String_": "ja-JP"
       }
      },
      "location": {
       "Value": {
        "String_": "Osaka"
       }
  },

Referring to my struct above, I'd like a format as such:

 [
  {
    "Id": 12353,
    "Language": "ja-JP",
    "Location": "Osaka"
  },
  // .. other objects
 ]

Assuming the same input to the func transformJSON, how would I match the nested keys with the column type values as well?

Should I Marshal the map first, then transform the data -- or work directly with the []map[string]*sql.SqlCell data structure before marshal?

In my head, I was thinking along the lines of:

func transformJSON(extract []map[string]*sql.SqlCell) ([]byte, error) {
    struct :=[] myStruct{}
    // Loop over extract objects, match nested keys, write to struct?

    return json.MarshalIndent(struct, "", " ")
}

Answer 1

Create a custom unmarshaler, that unmarshals the entire thing, then converts for you:

type MyStruct struct {
    ID                  int    `json:"Id"`
    Language            string `json:"Language"`
    Location            string `json:"Location"`
}

type val struct {
    Value struct {
        String string `json:"String_"`
        Long   int    `json:"Long"`
    }
}

func (s *MyStruct) UnmarshalJSON(p []byte) error {
    var result struct{
        ID       val `json:"Id"`
        Language val `json:"language"`
        Location val `json:"location"`
    }
    if err := json.Unmarshal(p, &result); err != nil {
        return err
    }
    s.ID = result.ID.Value.Long
    s.Language = result.Langauge.Value.String
    s.Location= result.Location.Value.String
    return nil
}

Note that minimal error checking and data validation is done in this example--I leave that as an exercise for the reader.